Providing security for a door has been a concern over centuries. The earliest known mechanical lock for a door can be traced back to early Egyptian times over 4,000 years ago. The early Egyptians employed a sliding wooden bolt through a stationary staple. The staple contained vertically positioned pin tumblers which extended into corresponding holes in the bolt when locked. The key was a curved, flattened wooden stick with pins projecting from one end. This end of the key was inserted into a hollowed portion of the bolt and maneuvered upwardly to push the pins from the bolt. The bolt then could be withdrawn to unlatch the door.
By the 13th Century, a metal warded lock which was first developed by the Romans, became very popular throughout Europe. This type of lock required that a key must be made to bypass the wards of the lock. Once bypassed, the key could then be turned to operate the latch. During the 18th Century, the tumbler lock was invented. Similar to the principal of the early Egyptian lock, the tumbler could be raised an exact height to clear its slot. This lock remains as the basis for modern locks today with the only difference being the use of multiple tumblers. Although lock and keys are still an effective way of controlling access to a building structure or a restricted area therein, the issuance of a key or a set of keys to numerous personnel has become impractical.
In general, modern door locks are used in conjunction with a conventional latch bolt assembly which is installed on a standard door. The latch bolt assembly includes a spring latch bolt and often includes a dead latch bolt that enables and disables movement of the spring latch bolt. The spring latch bolt is spring biased to extend from the door and into a latch bolt receiving cavity in the doorjamb when the door is in a closed position. The dead latch both is spring-biased outwardly from the latch assembly, but, when the door is secured, the dead latch bolt is depressed to disable retraction of the spring latch bolt. The spring latch bolt is slideably movable between an extended state and a retracted state and the dead latch bolt is slideably movable between an enable state and a disable state. In the enable state, the dead latch bolt permits the spring latch bolt to move from the extended state to the retracted state. In the disable state, the dead latch bolt prohibits the spring latch bolt from moving from the extended state to the retracted state. Typically, a strike plate is used to retain the dead latch bolt in its disable state unless a computerized security system is employed.
When security is required to control access through a door, especially one that is provided with the standard latch assembly described above, it is known to employ a computerized security system. Here, anyone with a valid key card or an authorized access code can gain access through secured doors. With the advent of computers, each person can have his/her own key card or access code so that a person may be authorized to gain access through one, all or a specified number of doors. If, for example, the key card is lost or stolen, that particular key card could be canceled and a new key card with a new access code could be issued.
In a computerized system, an electronic strike is activated when the appropriate access code is detected so that the person having a valid key card may enter through the door. In general, this electronic strike includes a single-lobed cam that pivots between a door lock position and a door release position. In its door lock position, the cam is positioned to simultaneously capture the spring latch bolt and the dead latch bolt with the spring latch bolt projecting into its extended state and and with the dead latch bolt retained in its disable state. In the door lock position, a pin from an electrically-powered solenoid extends into a recess in the cam to prevent movement of the cam from pivoting out of its door lock position. When the correct access code is detected, the pin from the solenoid withdraws from the recess in the cam so that the cam is free to pivot away from the latch as the door is pulled open. After the latch bolt assembly clears the cam, it springs back into its original position and, after a few seconds, the pin of the solenoid once again is extended into the recess of the cam to retain the door in its closed position.
A problem associated with this solenoid-type electric strike is that, if a user is pulling on the door at that time when the computer sends the electric signal to release the strike, the strike might not release. Pulling on a door results in pulling on the extended latch. The extended latch, in turn, applies back pressure against the cam being held by the solenoid pin in the door lock position. Now, the solenoid pin is unable to be withdrawn from its recess due to this back pressure. Thus, the pin cannot release thereby preventing the door from being opened.
Furthermore, installation of such a strike device for an existing, unsecured door requires substantial modifications to the doorjamb. Not only must the side portion of the doorjamb be modified but also the front portion of the doorjamb must be modified. This results in the electric strike being exposed so that now an intruder may use a lever against the cam to break the solenoid pin of the door latch actuator for easy entry because there is no face plate or other protective mechanism to encase the electric strike.
A need exists in the marketplace to provide a door latch actuator that is easy to install into existing doorjambs without making major modifications thereto. It would be beneficial if the door latch actuator is simple and inexpensive to manufacture. There is also a need to provide a door latch actuator that can provide a higher measure of security to prevent easy breaking and entering as compared to existing electric strike devices. It would be advantageous to provide a door latch actuator that can employ conventional components such as the strike plate that is presently being used on the doorjamb. The major benefit of using prior art components is that non-secured doors can now be easily retro-fitted as secured doors. Also, reducing installation time of the door latch actuator would be beneficial. It is from these considerations and others that the present invention has evolved.